Tree stump grinder

ABSTRACT

A tooth ( 30 ) for use in a grinding wheel is provided. The tooth comprises a main body ( 31 ) including a slot ( 32 ) comprising two substantially planar surfaces for, in use, engaging with a slot ( 24 ) in the rotor ( 20 ), and at least one cutting face ( 33, 34, 35, 36 ) connected to and extending away from the main body. In use, the force in the plane of the rotor is transferred from the tooth onto the rotor via one of the planar surfaces provided on the slot.

The present invention relates to tree stump grinding machines andparticularly to the grinding wheel of such a machine and the associatedtooth design.

It is known in the prior art to provide a tree stump grinding machinewith a cutting wheel driven by a belt, a chain, shafts or hydraulicmotors. Such machines are also referred to as cutting machines in someregions. Throughout the specification the term grinding machine will beused. Current stump grinding machines consist of a, typically circular,wheel with a number of receiving brackets positioned around the rim. Thereceiving brackets have channels into which are fitted individualcutting teeth. Each tooth is individually mounted and a gauge is oftenrequired to set each tooth at the correct distance from the centre ofthe wheel. Each tooth is held in place by retaining bolts that aretightened to a very high degree in order to hold the teeth. The boltsand retaining brackets are required to take the full rotational force ofthe grinding action. The wheel is provided with a plurality of teeth,some of which are fitted to cut vertically while others are fitted tocut horizontally, as the wheel moves along a horizontal and verticalaxis. An example of such a grinding wheel is found in U.S. Pat. No.6,484,766.

The teeth and receiving brackets provided on the grinding wheels knownfrom the prior art have to be changed regularly as a result of theconsiderable wear that they encounter in use. Changing the teeth andreceiving brackets is time consuming because of the set up accuracyrequired. Each tooth is generally held in place using two bolts tosecure the receiving bracket and the tooth. The task of changing theteeth is invariably complicated by the earth and mud that clogs theteeth, brackets and bolt threads which then require cleaning prior tofitting of a new tooth. As a result of the earth and mud, the receivingthread in the cutting wheel and the bolt or bolts may becomecross-threaded and require repair before a new tooth can be fitted. Inaddition to the expense incurred in a long down-time to change theteeth, the teeth and receiving brackets themselves are expensive becauseof the number of heavy duty components.

U.S. Pat. No. 6,550,504 shows an example of how a plurality of teeth canbe attached to a rotor. Each tooth consists of a cutting tip and bodyportion. The body portion includes two holes that allow the tooth to beattached to the rotor and the rotor is provided with corresponding pairsof holes for attaching the teeth by suitable fixing means, typicallybolts, that pass through the tooth and the rotor and is then secured,typically using a nut that screws onto the bolt. In this way the toothis mounted on the rotor.

There are two forces acting on the tooth that are of importance in thiscontext. The first is the sheer force that prevents the tooth fromslipping around the rotor and that arises because the tooth is not inthe plane of the rotor. The second force is the bending moment which isa function of the distance between the fixing means and the cutting tip.In the example shown in U.S. Pat. No. 6,550,504 the cutting tips arepositioned considerably out of the plane of the rotor and therefore thebolt that attaches the tooth to the rotor will experience both thebending moment caused by the distance between the tip and the bolt and,in addition, the sheer force acting across the bolt.

U.S. Pat. No. 6,546,977 discloses a stump grinding device that reducesthe force on the bolt by providing a cutting unit that is disposed inthe plane of the rotor. Therefore the bending moment is considerablyreduced in comparison with the example shown in U.S. Pat. No. 6,550,504.However, the sheer force across the bolt remains the means by which theforce is transferred from the cutting tip to the rotor.

U.S. Pat. No. 6,375,106 discloses a machine that is designed to reducewaste by grinding. Although this is not the same technical field as theother art, some similar problems will be encountered. The teeth arereplaceable and, unlike the previously discussed prior art, theattachment device is in the plane of the rotor. However, the tortuouscross section of the attachment device and locking element result inconsiderable stresses on certain parts of the interface between therotor and the cutting tip.

According to the present invention there is provided a tooth for use ona grinding wheel, the tooth comprising

a main body including a slot defining two opposed substantially planarsurfaces for, in use, engaging with a slot in the rotor,

at least one cutting face connected to and extending away from the mainbody;

whereby, in use, the force in the plane of the rotor is transferred ontothe rotor via one of the planar surfaces provided of the slot.

The slot allows for the use of a single low cost bolt to keep the toothin place. The tooth may be a multi-tipped tooth which may haveprotruding transverse tips to facilitate lateral grinding, in additionto radial tips. Such a multi-tipped tooth allows for cutting in radialand lateral directions simultaneously.

Preferably, the plurality of cutting tips includes at least two tipswhich are perpendicular to each other. The tooth may furthermore beprovided with a through hole through which a fixing means may pass, inuse and a channel in its back face.

The fixing means is typically a single low cost standard bolt with alocking nut and is a “throw away” item which can be changed every time atooth is changed. This means that there is no cleaning required andtherefore the problems with cross-threading encountered in the prior artare effectively overcome.

The transfer of the forces from the tooth to the rotor may be directlyfrom the planar surfaces of the slot in the tooth on to the planarsurfaces in the slot in the rotor. Alternatively, a keeper plate may beinterposed between the slot in the tooth and the corresponding slot inthe rotor. The keeper plate has the added advantage of being able toprovide a means for screwing the bolt into the rotor and therebytightening the tooth as it wears loose, in use. During the tighteningprocess there is no relative movement between the keeper plate and thetooth. Instead, the keeper plate and tooth move together relative to theslot in the rotor. The underside of the tooth is provided with a taperedsurface that interfaces with one of the planar surfaces that comprisethe slot in the rotor. Therefore as the bolt is screwed into the rotorthis causes relative movement between the tooth and the rotor thustightening the tooth and preventing it from moving relative to thekeeper plate. The taper is preferably the same on both surfaces and isgenerally around 11°.

Furthermore, in accordance with the present invention there is provided,a grinding unit for use with a grinding machine, the unit comprising:

a rotor having a rim around which a plurality of slots are provided;

a plurality of teeth, each tooth having a slot for engagement with oneof the slots in the rotor; and

fixing means for retaining each tooth in its associated slot in therotor.

The provision of co-operating slots on the teeth and rotor rim obviatethe need for precise set-up required by the grinding units of the priorart. Furthermore, the fixing means is required only to retain the toothin place as the wheel itself absorbs a substantial proportion of theforces in the plane of the rotor resulting from the grinding action.

The radius of the rotor may vary around the circumference. In particularthe shape of the rotor may be that of a polygon that may be irregular.Preferably the rotor has an even number of sides and preferably there isa slot provided at each corner of the polygon.

The polygonal shape of the rotor allows the teeth to be positioned atdifferent distances from the axis of rotation of the rotor. A rotor withan even number of sides is preferable as it facilitates easy balancingof the wheel. If the slots were not provided at the corners of thepolygon, there would be sections of the polygon extending further thanthe teeth and these would, in use, impact on the stump to be ground,causing damage to the grinding unit.

When the term “slot” is used in this specification it is intended torefer to any physical configuration that provides two planar surfacesthat enable the interlocking of a second piece. In particular a simpleslot may be provided in the circumference of the rotor by cutting asubstantially U-shaped gap in the periphery of the rotor thus providingtwo substantially planar surfaces into which a tooth may be slotted inuse. Alternatively, the slot may be formed by the provision of matchingpairs of protrusions on the sides of the rotors that have the combinedeffect of providing a slot on the side of the rotor. These protrusionsmay be welded on or may be cast as part of the rotor itself.

Preferably the slots are arranged in diametrically opposed pairs whereinthe slots in an opposing pair of slots are the same distance from theaxis. Preferably, the slots are arranged in two diametrically opposedseries, each successive slot in each series having an increased distancefrom the axis.

The arrangement of the slots in diametrically opposed pairs equidistantfrom the axis of the rotor allows the rotor to be more easily balanced.Furthermore, this allows two series of teeth to be developed eachcovering 180/of the rotor. The teeth are located in the slots at thecorners of the rotor and therefore, as a result of the differences incircumference of the rotor different teeth extend different distancesfrom the axis of rotation of the rotor. As a result of the twodiametrically opposed series, the stump is, in use, successively groundby teeth that extend further from the axis. If such a sequence of toothdiameters is used then it is clear that there is one correct directionof rotation for the rotor. The teeth that extend furthest from the axisdo more of the cutting and those set further in towards the axis act asrestrictors. This configuration of teeth also enables a sideways or slewcut to be achieved.

The number of slots is preferably 4, 6, 8, 10 or 12. Some or all of theslots may be angled either towards or away from the axis of rotation ofthe rotor. If the slots are angled towards the axis of rotation, theteeth will protrude perpendicular to the rim of the rotor and therefore,dependent on the configuration of the cutting tips of the teeth, therotor could be rotated in either direction. However, if the slots areangled away from the axis of rotation the teeth will protrude at anangle. In this case, the rotor will function correctly with only onedirection of rotation. This is particularly useful in the case when theslots have been configured such that the tree stump is ground with teeththat protrude progressively further from the axis of rotation over arange of 180°.

The present invention will now be further described with reference tothe accompanying drawings in which:

FIG. 1 shows a tree stump grinding machine incorporating a grinding unitaccording to the present invention and a plurality of teeth according tothe present invention;

FIG. 2A shows a cross-section of a rotor and FIG. 2B shows the rotorfitted with a number of teeth;

FIGS. 3A and 3B show perspective views of a single tooth; and

FIGS. 4A and 4B show perspective views of a further example of a singletooth.

FIG. 5 shows a further example of a rotor with a slot;

FIG. 6 shows a further example of a slot in the rotor;

FIG. 7 shows a further example of a tooth and corresponding slot in therotor;

FIGS. 8 and 9 show a grinding wheel including a keeper plate.

FIG. 1 shows a grinding machine 100 comprising a support arm 10, a rotor20 and a plurality of teeth 30. The arm 10 forms a housing for atransmission which may be a belt, chain drive shaft or hydraulic motor.The rotor 20 is caused to rotate by a driving engine 39 that transmitsthe power via the transmission housed in the support arm 10. The rotor20 is attached a central hub 22 which passes through a set of bearingscontained within a bearing housing 21 which is attached to the arm 10.As shown in FIGS. 2A and 2B, around the rim 23 of the rotor 20 are aplurality of slots 24 located on the corners of the rim. Radiallyinwardly of each of which there is provided a respective hole 25. Therotor 20 is octagonal, although almost any polygonal shape may be used,in particular a hexagon or decahedron. Each of the slots 24 andrespective holes 25 is used to accommodate a tooth 30. A fixing boltpasses through the tooth 30 and through the hole 25 in the rotor 20 inorder to secure the tooth 30 in position on the rim 23 of the rotor 20.

FIG. 2A shows a cross section of the rotor 20 and FIG. 2B shows therotor 20 fitted with teeth 30. Eight teeth 30 are provided, one at eachcorner of the rotor 20. The irregular shape of the rotor results in theteeth 30 not being equidistant from the hub 22 of the rotor 20. Theteeth are arranged in two series, each covering 180° of the rotor 20wherein the distance of each tooth 30 from the axis of rotation isgreater than the adjacent tooth in the direction in which the rotorrotates, in use. In use, the teeth 30 of the resulting rotor 20 grind alittle more of the tree stump as each tooth 30 comes to make contactwith the tree stump. This allows the grinding machine 100 to grind treestumps more efficiently as a deeper side (slew) cut is achieved as thearm's cutting motion is sideways.

FIGS. 3A and 3B show a tooth 30 that has a body 31, a slot 32 and aplurality of cutting tips 33, 34, 35 and 36. The slot 32 has a hole 37through which, in use, a bolt 27 passes to secure the tooth 30 onto therotor 20. A nut 28 may be used to lock the bolt 27 in place.Alternatively, if the hole 37 in one side of the tooth is threaded it isnot necessary to use a nut 28. The slots 24 on the rotor 20 interfacewith the slots 32 on the teeth 30 through the abutment of back and frontplanar surfaces 38, 38 a of the tooth 30 with adjacent planar surfacesthat form the slot 24 of the rotor 20. This interface allows a largeproportion of the force in the plane of the rotor to be communicateddirectly onto the rotor 20 rather than communicating these forcesthrough the fixing means. The bolt does not communicate the forces andis required to prevent the tooth from being discharged throughcentrifugal force alone. The four tips (33 to 36) are arranged in twoorthogonal pairs allowing efficient cutting in radial and lateraldirections simultaneously.

As shown in FIG. 3A the tooth 30 is also provided with a shallow channel38 in the back face that forms the planar surface that allows the rotor20 to take up forces from the tooth 30 in the lateral plane.

The through hole 37 may be provided on any part of the tooth 30 as theforces are communicated to the rotor 20 through the slots 24, 32 on thetooth 30 and the rotor 20 and the through hole 37 is not required forthis function. The role of the through hole 37 in preventing the toothfrom disengaging from the rotor 20 may be fulfilled regardless of thepositioning of the through hole 37. Further protrusions or holes may bedesigned into the tooth to secure it into the rotor 20.

An alternative configuration of a tooth is shown in FIGS. 4A and 4B.This tooth 40 is provided with a pair of protrusions 41, 42 that extendradially along the rim. The tooth 40 interfaces with a slot 24 in arotor 20 and the protrusions secure the tooth 40 to prevent it fallingout. Although this configuration has less lateral stability than thetooth 30 shown in FIGS. 3A and 3B it is capable of communicating theforces to the rotor 20 as described above with reference to FIGS. 3A and3B.

FIG. 5 shows a further example of a tooth 30 according to the presentinvention. The tooth 30 comprises a body 31 provided with a slot 32 andhole 37 similar to those shown in FIGS. 3A and 3B. However, instead of aplurality of cutting tips 33 to 36 the tooth is provided with a singlecutting face 53 which is “C” shaped which enables the cutting face 53 tocut in two perpendicular planes. The cutting face has a less tortuouscross section than the individual tips shown in FIG. 3 and therefore hasa larger cutting surface for the same lateral extension from the rotor.As a result of this larger cutting surface, a larger volume of materialcan be removed at any one time.

FIG. 6 shows a further example of a slot in the rotor. The slots 64, 65are provided as a matching pair of slots that are formed by protrusions66, 67, 68, 69 that extend from the surface of the rotor 20. One pair ofthe protrusions 66, 67 are positioned on a first side of the rotor andthe other two protrusions 68 and 69 are positioned on the opposite sideof the rotor. Between them, each pair of protrusion form a narrowchannel or slot. The protrusions 66 to 69 extend towards the centre ofthe rotor 20 and extend beyond the position of the hole 25 by which thetooth 30 is secured onto the rotor 20, in use. Pairs of slots 64, 65 maybe added to the rotor 20 after it has been formed or may be formedintegrally with the rotor.

FIG. 7 shows a tapered tooth 70 and a corresponding tapered slot 24 inthe rotor 20. The tooth 70 functions in the same way as the tooth 30shown in FIGS. 3 and 4 in that the forces exerted on the tooth 70 in theplane of the rotor 20 are transferred to the rotor 20 via one of theplanar surfaces of the body of the tooth 70. However, instead ofproviding through holes 37 in the slot 32 of the tooth 30, there isprovided a hole 77 through the body of the tooth 70 in the radialdirection, as the tooth 70 rests in the slot 24 of the rotor 20. Inorder to prevent the tooth 70 from flying out of contact with the rotor20 a bolt 76 is provided that passes through the hole 77 in the tooth 70and into a corresponding hole 25 in the rotor 20. The body of the tooth70 is tapered. The taper 78 provides a broader tooth cross-sectioncloser to the cutting tips 73 of the tooth 70 and a narrower toothcross-section closer to the centre of the rotor 20 when the tooth 30 ispositioned for use on the rotor 20. The slot 24 in the rotor 20 is alsoprovided with a taper that matches the taper 78 on the tooth 30.

FIGS. 8 and 9 show a grinding wheel including a keeper plate 80. Thekeeper plate 80 is shown in FIG. 8 in position between the tooth 30 andthe rotor 20. The keeper plate 80 is suitable for higher powerapplications in which the forces on the tooth 30 are greater than inlower power applications. The keeper plate is a generally U-shapedmember that abuts the tooth 30 and enables the tooth 30 to be tightenedrelative to the rotor 20. The keeper plate 80 has two leg portions 81,82 which, in use, abut the sides of the rotor 20. The legs 81 of thekeeper plate extend transversely beyond the edge of the slot 24 in therotor 20. This prevents any movement in the plane perpendicular to theplane of the rotor 20. The keeper plate 80 is also provided with a lug83 which interfaces with a notch 84 in the upper surface of the tooth30, in use. The keeper plate 80 is also provided with a bore 85 andcounter bore (not shown) arrangement that enables a bolt 86 to bescrewed through the bore 85 in the keeper plate and into the hole 25provided in the rotor 20.

The tooth is further provided with a tapered surface 87. The taper 87 isradial and provides a broader tooth cross-section closer to the tip ofthe tooth and a narrower tooth cross-section closer to the centre of therotor when the tooth 30 is positioned for use on the rotor 20. The slot24 in the rotor 20 is also provided with a taper that matches the taper87 on the tooth 30.

When the tooth 30 is initially fitted into the rotor 20 the bolt 86 isscrewed into the keeper plate so that the tooth 30 is held securely.After the tooth 30 has been used in the rotor 20 for some time the tooth30 will work loose and begin to move slightly relative to the rotor 20.When this occurs the bolt 86 may be tightened so that the keeper plate80 and tooth 30 move together radially inwardly toward the centre of therotor 20. As a result of the tapered surface 87 on the lower part of thetooth and matching taper on the slot 24 in the rotor 20 the tooth 30will be tighten into position on the rotor 20.

FIG. 9 shows the tooth 30 being replaced. It is not necessary to removethe bolt 86 entirely from the keeper plate 80 and therefore the keeperplate 80 remains attached to the rotor 20 throughout the replacement ofthe tooth 30. Instead, once the bolt 86 has been loosened there will besufficient movement possible between the rotor 20 and the keeper plate80 allow the tooth 30 to fall out of position and to be replaced by anew tooth.

The keeper plate 80 is made from a metal that is soft is comparison withthe metal of the rotor 20 and tooth 30 and therefore the keeper plate 80will wear more quickly than the rotor 20 and can be replaced moreconveniently. The use of a keeper plate 80 thereby increases the usefullife of the rotor 20.

1. A tooth for use in a grinding wheel having a rotor, the toothcomprising: a main body including a slot comprising two substantiallyplanar surfaces for, in use, engaging with a slot in the rotor, at leastone cutting face connected to and extending away from the main body;wherein, in use, the force in the plane of the rotor is transferred ontothe rotor via one of the planar surfaces provided on the slot; andwherein the cutting face includes at least two tips which areperpendicular to each other.
 2. A tooth according to claim 1, furthercomprising a channel in its back face.
 3. A tooth according to claim 1,further comprising a through hole for alignment with one of a pluralityof through holes in the rotor when the tooth is located in one of theslots in the rotor.
 4. A grinding unit for use with a grinding machine,the unit comprising: a rotor having a rim around which a plurality ofslots are provided; a plurality of teeth, each tooth comprising: a mainbody including a slot comprising two substantially planar surfacesengaged with a respective slot in the rotor, at least one cutting faceconnected to and extending away from the main body; wherein, in use, theforce in the plane of the rotor is transferred onto the rotor via one ofthe planar surfaces provided on the slot; and wherein the cutting faceincludes at least two tips which are perpendicular to each other; andfixing means for retaining each tooth in its associated slot in therotor.
 5. A grinding unit according to claim 4, wherein the radius ofthe rotor varies around the circumference.
 6. A grinding unit accordingto claim 4, wherein the rotor is polygonal.
 7. A grinding unit accordingto claim 6, wherein the polygon shape is irregular.
 8. A grinding unitaccording to claim 6, wherein the rotor has an even number of sides. 9.A grinding unit according to claim 6, wherein each slot is provided at acorner of the polygon.
 10. A grinding unit according to claim 8, whereinthe slots are arranged in diametrically opposed pairs.
 11. A grindingunit according to claim 10, wherein the slots in an opposing pair ofslots are the same distance from the axis.
 12. A grinding unit accordingto claim 8, wherein the number of slots is 4, 6, 8, 10 or
 12. 13. Agrinding unit according to any one of claims 4 to 12, wherein at leastone slot is angled towards the axis of rotation of the rotor.
 14. Agrinding unit according to any one of claims 4 to 12, wherein at leastone slot is angled away from the axis of rotation of the rotor.
 15. Agrinding unit according to claim 12, wherein the slots are arranged intwo diametrically opposed series, each successive slot in each serieshaving an increased distance from the axis in the direction in which therotor rotates, in use.
 16. A grinding unit according to claim 4, whereinthe rotor further comprises a plurality of through holes correspondingin number with the number of slots in the rotor, and each tooth furthercomprises a corresponding through hole in alignment with a respectivethrough hole in the rotor when the tooth is located in the respectiveslot on the rotor, and wherein the fixing means is a nut and bolt, thebolt passing through the aligned through holes in the rotor and therespective tooth.